The three legal concepts that turned a reasonable self-defense law into a recipe for vigilante justice.

The Florida law made infamous this spring by the killing of unarmed teenager Trayvon Martin was conceived during the epic hurricane season of 2004. That November, 77-year-old James Workman moved his family into an RV outside Pensacola after Hurricane Ivan peeled back the roof of their house. One night a stranger tried to force his way into the trailer, and Workman killed him with two shots from a .38 revolver. The stranger turned out to be a disoriented temporary worker for the Federal Emergency Management Agency who was checking for looters and distressed homeowners. Workman was never arrested, but three months went by before authorities cleared him of wrongdoing.

That was three months too long for Dennis Baxley, a veteran Republican representative in Florida's state Legislature. Four hurricanes had hit the state that year, and there was fear about widespread looting (though little took place). In Baxley's view, Floridians who defended themselves or their property with lethal force shouldn't have had to worry about legal repercussions. Baxley, a National Rifle Association (NRA) member and owner of a prosperous funeral business, teamed up with then-GOP state Sen. Durell Peaden to propose what would become known as Stand Your Ground, the self-defense doctrine essentially permitting anyone feeling threatened in a confrontation to shoot their way out.

Or at least that's the popular version of how the law was born. In fact, its genesis traces back to powerful NRA lobbyists and the American Legislative Exchange Council (ALEC), a right-wing policy group. And the law's rapid spread—it now exists in various forms in 25 states—reflects the success of a coordinated strategy, cultivated in Florida, to roll back gun control laws everywhere.

Baxley says he and Peaden lifted the law's language from a proposal crafted by Marion Hammer, a former NRA president and founder of the Unified Sportsmen of Florida, a local NRA affiliate. A 73-year-old dynamo who tops off her 4-foot-11 frame with a brown pageboy, Hammer has been a force in the state capital for more than three decades. "There is no more tenacious presence in Tallahassee," Gov. Jeb Bush's former chief of staff told CNN in April. "You want her on your side in a fight."

Ever since neighborhood watch volunteer George Zimmerman shot Trayvon Martin point-blank in the chest, the term Stand Your Ground has been widely discussed, but what does it really mean? A Mother Jones review of dozens of state laws shows that the concept is built on three planks from the pioneering Florida legislation: A person claiming self-defense is not required to retreat from a threat before opening fire; the burden is almost always on prosecutors to prove that a self-defense claim is not credible; and finally, the shooter has immunity from civil suits relating to the use of deadly force. While the so-called Castle Doctrine (as in "a man's home is his") has for centuries generally immunized people from homicide convictions if they resorted to deadly force while defending their home, Florida's law was the first to extend such protection to those firing weapons in public spaces—parking lots, parks, city streets.

Stand Your Ground was shepherded through the Legislature with help from then-state Rep. Marco Rubio and signed into law by Bush on April 26, 2005. It was the "first step of a multi-state strategy," Wayne LaPierre, a long-standing NRA official who is now the group's CEO, told the Washington Post. "There's a big tailwind we have, moving from state legislature to state legislature. The South, the Midwest, everything they call 'flyover land.'" The measure was adopted as model legislation by ALEC, a corporate-sponsored national consortium of lawmakers—which is how it ended up passing in states from Mississippi to Wisconsin. "We are not a rogue state," says Baxley, who was bestowed with the NRA's Defender of Freedom Award shortly before his bill passed. "But we may be a leader."

Supporters of such laws cite the slippery-slope argument: Seemingly reasonable regulations—waiting periods, licenses, limits on assault weapons and high-capacity magazines—inevitably lead to ever-stricter measures, they argue, until citizens' constitutional right to defend themselves against government tyranny has vanished. Hammer suggests that an assault on gun rights motivated her move to Tallahassee from her native South Carolina in 1974: "Florida was seeing what I would call a burst of gun control measures being filed by Northerners who had moved to South Florida," she told a radio interviewer in 2005. "There was so much gun control being filed that it was very difficult for the NRA to deal with it from over 1,000 miles away."

After leaving work late one night in the mid-1980s, Hammer claims, a group of men in a car threatened her, only to be scared off when she pulled a gun on them. No police report was ever filed, but Hammer maintains that shortly after this incident a local police chief told her that she could have been arrested had she shot them. It was a convenient tale. She soon became a driving force behind Florida's "shall issue" legislation, passed in 1987, which stripped authorities of the ability to deny a concealed-weapons permit to someone they consider potentially dangerous.